Commercial fructose-containing syrups are manufactured by the enzymatic isomerization of glucose obtained from corn-derived starch hydrolyzates. This is usually accomplished in a continuous process which involves contacting the glucose-containing solution with a glucose isomerase enzyme preparation that has been immobilized in some fashion. These procedures give a syrup in which fructose is less than 50%, usually 40-45%, of the total carbohydrate present.
Because fructose is sweeter than either glucose or sucrose, much effort has gone into developing processes for producing syrups in which more than 50% of the carbohydrate is fructose. Typically, these methods have involved chromatographic procedures for separating the fructose from the other carbohydrates contained in syrups derived from sucrose and/or corn. Examples are U.S. Pat. Nos. 4,096,036, 4,022,637 and 3,483,031.
Recently, a novel way to obtain fructose syrup of greater than 50% fructose content was disclosed in British Patent Specification No. 2,000,144. According to that procedure, a sucrose substrate is subjected to the action of a fructosyl transferase enzyme to convert the sucrose to an intermediate syrup containing predominantly fructose polymers and glucose. This syrup, in which the fructose is in polymeric form, is useful as a specialty carbohydrate or it can be further treated to produce fructose syrups of greater than 50% fructose content. About half of the glucose in the intermediate syrup can be isomerized to fructose by means of a glucose isomerase enzyme. Subsequent hydrolysis of this reaction mixture cleaves the fructose polymers to fructose, thereby producing a high fructose syrup containing a major amount of fructose and minor amounts of glucose.